The objective of this multicenter double-blind, placebo controlled randomized study is to evaluate the safety and efficacy of multiple doses of r-h CuZnSOD to prevent oxygen toxicity & severe lung disease in neonates who require mech. vent. At present there is only symptomatic tx for oxygen toxicity. Surfactant therapy improves RDS (Resp. Distress Syndrome) but not PBD (Bronchopulm. Dysp.), a chronic inflammatory condition of the lungs triggered by exposure to O2 in premature infants, who are known to have very reduced levels of antioxidant enzymes.